Biofeedback lifting monitor

ABSTRACT

An apparatus for testing and teaching the lifting capacity and technique of a user includes a brake or clutch for resisting user input force which is controlled by feedback from sensors through a computer. Several operating modes can be chosen, including isometric, isokinetic, isotonic and a special accommodating isotonic which simulates lifting a real object as long as the user exerts enough force, but decreases a resisting force when it is more than the user can handle. A motor is used to substantially eliminate inherent system resistance.

DESCRIPTION

1. Technical Field

The present invention relates generally to an apparatus for measuring aperson's lifting capacity, and in particular a clinical apparatus fordetermining a patient's minimum and maximum lifting capacities. It alsorelates to apparatus for teaching clinicians and patients proper liftingtechniques.

It has been a long-standing problem of clinicians to objectivelydetermine when a patent can return to work following a back injuryrelated to lifting. Clinicians must also determine the potential forre-injuring a patent who has suffered from a back injury related tolifting. The possibility of re-injury has become a growing concern ofmedical liabiality. A medical clearance with special provisions isfrequently required by an employer before an employee can return to workafter such a back injury.

It has been a common practice to assign lifting provisions subjectively,such as 20-25 pounds maximum lifting limit. Physical functionsassessments are difficult to quantify, and it is likewise difficult todetermine if a patient is actually meeting the minimum job requirements.Nonetheless, it is frequently assumed by both the patient and theemployer that so long as the patient abides by the lifting provisions,it is safe to return to the work place.

Health related standards have been formulated which require the patientbe statistically strength tested in an isometric (no movement) mode. Thepatient pulls on a strain gauge in a given static posture and themeasurement is then compared to a standard. The validity of thisapproach is repeatedly questioned due to comparing the result of anisometric test in evaluating a dynamic event.

1. Background Art

In recent years, there have been attempts to provide strength testingdevices for dynamic testing. Some of these devices would involvedeveloping isokinetic exercise apparatus of which the user moves at aconstant velocity regardless of the amount of resistance that isapplied. The isokinetic exercise allows the user to move throughout anentire range of motion safely, because the force offered by theapparatus is accommodating to the user force.

Conceptionally, isokinetic exercise is similar to pushing against an airpump piston. If a user could regulate the amount of air exiting thepump, then when the user pushes hard on the air pump, there would be agreat amount of back pressure and thus the person would encounter agreat amount of resistance. If the user pushes only slightly on the airpump, then the user would encounter only a slight amount of resistance.Whether the user pushes hard or slow against the piston, the pistonmoves at a substantially constant speed, and thus the accommodatingconcept of isokinetics. Such devices are shown in U.S. Pat. Nos.4,041,760 of Henson, et al, 3,896,672 of Henson, et al and 3,465,592 ofPerrine.

Another advantage of the isokinetic mode is that it allows a clinicianwith no prior familarity with the patient's strength capabilities totest the patient by simply placing him or her in an isokinetic mode. Theclinician can safely ascertain the patient's strength capabilities. Adisadvantage and criticism of the isokinetic mode is, however, that itdoes not simulate normal movement. A person does not normally move at aconstant velocity. In normal lifting, a person accelerates at thebeginning of the lifting stroke and decelerates toward the end of thestroke. For this reason, there have been inventions that have addressedthe need to operate in an isotonic (constant force) mode. For example,U.S. Pat. No. 3,902,480 of Wilson has provided an electrical-mechanicalisotonic or isokinetic exercise system. U.S. Pat. No. 4,184,678 ofFlavell et al shows a programmable acceleration excerciser. In thisapparatus, Flavell has provided means for the user to choose among avariety of pre-selected acceleration and constant velocity patterns.U.S. Pat. No. 4,138,106 of Bradley shows a weight training apparatus inwhich the force varies according to the initial acceleration. The useris not, however, able to choose a pre-selected force and acceleratefreely in either Flavell or Bradley systems. U.S. Pat. No. 4,544,154 hasprovided a programmable isokinetic or isotonic system with a feedbackloop using hydraulic components. Once the user chooses a pre-selectedforce at the beginning of the test, the feedback loop maintains thatforce regardless of the varying velocities.

Although strength measurements are needed in any lifting analysis, theuse of a strength testing apparatus alone will not provide the clinicianwith the information needed in determining a "ready for work" status.The technique of lifting is one of the fundamental determinates topredicting back injury resulting from lifting.

There have been devices which measure joint ranges of motion. U.S. Pat.No. 3,929,335 of Malick was developed for the use of motivating apatient in need of occupational therapy to exercise. It includes hismovement and exercise of muscles after a long period of disuse for nervedamage. The exercises are often difficult and the patient must, in manycases, be constantly reminded to continue the exercise.

U.S. Pat. No. 4,108,164 of Hall relates to measuring the range of motionin the back with various activities. It includes a jacket containingclinometers. The sensors are attached to a jacket instead of to thesubject. Using this approach, there would be slippage between the jacketand the subject. The degree of slippage depends on how closely thejacket appromixates each individual. In addition, in the process oflifting, the concern is not necessarily with the spinal technique butrather in the hip and knee synchronization in general. As an example,during the lifting process, it is important that the knees are flexedsubstantially enough to allow the user's back to remain nearperpendicular to the floor in order to decrease the force on the user'sback.

DISCLOSURE OF INVENTION

In accordance with the present invention, an apparatus for testing andteaching the lifting capacity, of the user includes in a preferred forma handle and cable for user input. The user exerts force against thehandle which is affixed to the cable. The cable in turn rotates a shaft,but also operates on a force and angle measuring device. The user inputforce is resisted by some device such as a magnetic particle unit whichcan be either a brake or clutch. In one form, the testing and teachingapparatus includes a motor operably connected to the shaft forsubstantially eliminating inherent system resistance to the user inputforce. Biofeedback is provided to the user by a display device which ispositioned for user viewing as the user exerts force against the cableand handle.

In a preferred form, a computer controls the resisting apparatus. Theforce and angle measuring device as well as the device for measuring thedistance over which a user has exerted force are connected in a feedbackrelationship to the computer. The computer contains four program processsteps for operating the computer and program steps for selecting whichof the programs operates the computer at a given time. One program foroperating the computer produces substantially no movement resulting frominput force exerted by a user. A second program produces substantiallyconstant speeds throughout a predetermined portion of movement resultingfrom input force above a predetermined minimum exerted by user. Yetanother program limits the resisting force from the resisting device toa predetermined maximum, and the final program for operating thecomputer creates a substantially constant resisting force as long as theinput force exerted by user is at least a predetermined level and causesthe speed of movement resulting from input force exerted by user to beproportional to that force when that force is less than thepredetermined level. This particular program or process is referred tofor shorthand as an accommodating isotonic feature or mode. It allows auser to choose a pre-selected force and, through a feedback loop in theelectronic controller of the apparatus, the force will decrease orincrease according to the changes provided by the user. With theaccommodating isotonic mode, the user may select a weight to besimulated which acts only while the user is engaging the system. As longas the user is applying a force that is greater than or equal to thepre-selected force, the system will allow the user to freely accelerateor maintain a constant velocity depending upon the force input by theuser. If the user begins to decrease the full force, the velocity of thesystem will decrease until it has reached a full stop. If the user thenbegins to pull once again, then velocity continues to increase as itwould in a naturally occurring event. The system thus combines thesafety of the accommodating feature which has been previously availablewith isokinetics with the isotonic mode of movement.

These and other objects, advantages and features of this invention willbe apparent from the following description taken with reference to theaccompanying drawing, wherein is shown the preferred embodiments of theinvention.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a pictorial representation of a user operating the presentinvention;

FIG. 2 is a perspective view of a user input means, a resisting clutchor brake, sensors and buffer according to the present invention;

FIG. 3 is a diagrammatic view of the present invention showing means forsubstantially eliminating inherent system resistance and an alternativemethod for operably connecting the resistance brake or clutch;

FIG. 4 shows a combination force measuring and angle measuring unitaccording to the present invention;

FIG. 5 shows an exploded view of a joint position sensor;

FIG. 6 shows a cross-sectional view of the joint position sensor ofFigures;

FIG. 7 is a right side elevational view of an alternative embodiment ofan angle measuring device according to the present invention;

FIG. 8 is a front elevational cross-sectional view of the cabledirection sensor of FIG. 7;

FIG. 9 is a diagrammatic view of a lifting apparatus selection andoperational modes according to the present invention; and

FIG. 10 is a flow chart of a method for testing and teaching liftingcapacity and technique according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings and in particular to FIG. 1, a user 10begins a lift stroke on an apparatus 12 according to the presentinvention for testing and teaching his lifting capacity and technique.Apparatus 12 includes a platform 14 on which the user stands and somemeans for accepting user input force including a handle 16 for grippingand cable 18 secured to the handle. User input force can normally beexerted over a predefined distance from the start position until thecable is fully extended, normally with the user in a standing position.A system could also be constructed to allow the user to continue to liftthe handle over his head. Means, such as computer 20, is used forcontrolling and monitoring operation of the apparatus, and a hard copyof the results are provided by printer 22. A visual display 20D has aCRT screen 20CRT positioned for viewing by the user and thereby achievebiofeedback to the user of his lifting technique. This is helpful inteaching clinicians and users proper lifting techniques.

Referring now to FIG. 2, cable 18 extends through a slot 24 of platform14 and engages a spool 26 which is affixed to a shaft 28 which alsoforms part of the means for accepting user input force. Cable 18 windsaround spool 26, and unwinds as user 10 lifts handle 16, turning shaft28 as a result. Shaft 28 is rotably held on either side by pillowbearings 30. Cable 18 is also attached to force and angle measuringdevice 32. Readings from force and angle measuring device 32 as well asa rotation position sensor device 34 are connected in a feedbackrelationship to computer 20 through buffer 36 by pathways 38 and 40respectively. Rotation position sensor 34 acts as means for measuringthe distance over which a user has exerted force. . Means such asmagnetic particle unit brake or clutch 42 is in operably coupled toshaft 28 for resisting user input force. As a user engages the system,shaft 28 rotates so that rotation position sensor which is a shaftoptical encoder rotates and movement can be detected. Once the user hasreached the top of the lifting stroke, and begins letting handle 16 backdown, cable 18 is retracted by rewind coil 46 which operably engagesshaft 28. A one-way clutch 48 allows the shaft 28 to rotate in therewind direction without engaging magnetic particle unit brake or clutch42.

Referring now to FIG. 3, in an alternative arrangement in which likeelements are numbered the same as in previous figures, brake or clutch42 is operably coupled to shaft 28 through a chain and sprocketarrangement 50. Means including motor 52 is operably connected to shaft28 through chain and sprocket arrangement 54 which also drives rotationposition sensor 34. Motor 52 provides a positive rotation to shaft 28 asdirected by feedback path 56 in order to substantially eliminateinherent system resistance to user input force. This is distinct fromthose systems in which a motor provides the resistance in which therotation force of the motor is negative.

Referring also to FIG. 4, force and angle measuring device 32 includes aspool 58 which is driven by cable 18. Spool 58 is rotatably secured byhorizontal strut 60 and vertical strut 62 which are affixed to loadcells 64 and 66 respectively. Vertical load cell 66 abuts the lowersurface of platform 14 and measures the force in the vertical direction.Horizontal load cell 64 abuts a bracket 68 which is firmly affixed tothe bottom surface of platform 14, for measuring load in the horizontaldirection.

Referring now to both FIG. 1 and FIG. 3, hip positions sensors 70 andknee positions sensors 72 are attached to the body of user 10 by meansof lever arms 74 and cuff straps 76. Vertical sensor 78 is attached tothe waist of cuff strap. Inputs from all of these sensors are then fedto computer interface card 80, although buffering may be necessary. Thecomputer interface card 80 also receives inputs from rotation positionsensor 34 as well as horizontal and vertical load cells 64 and 66 whichhave been processed through buffer 36. Buffer 36 receives electricalpower from power supply 82 both to provide power to handle alltraditional converters 84 and 86 for converting the analog signal of theload cells to digital signals to be accepted by interface 80 and alsofor buffer amplifiers 88.

Referring also to FIG. 5 and FIG. 6, lower lever arm 74a forms a squareopening 90 for receiving square head 92 of nut 94. Upper lever arm 74bforms a circular opening 96 for receiving circular head 98. It can thusbe seen movement of lower lever arm 74a will in turn rotate code wheelassembly 100 of an optical motion encoder. Emitter assembly 102 of theoptical motion encoder is affixed to upper level arm 74b so that whenlever arm 74a rotates with respect to lever arm 74b code wheel assembly100 rotates with respect to emitter assembly 102. Bolt 104 rotatablyconnects the two lever arms. Encoder body 106 of the optical motionencoder houses the rest of the encoder and contains the phase place lensand detectors. The entire optical motion and coder is the type that iscommercially available and is also of a type similar to what is suitablefor rotation position sensor 34 (FIG. 3).

Referring now to FIG. 7 and FIG. 8, an alternative embodiment of anglemeasuring device according to the present invention is referred togenerally by reference numeral 108. Angle measuring device includes atube 110 through which cable 18 is pulled. Tube 110 is secured to shaft112 which is rotatably mounted along an axis perpendicular to the tube.Rotation of shaft 112, in turn, rotates the code wheel assembly withinan optical encoder 114. Movement of the angle pull of cable 18 thusrotates tube 110 about the axis of shaft 112 which in turn registers onoptical encoder 114.

Referring now to FIG. 9, an apparatus according to the present inventionfor testing and teaching the lifting capacity and technique of a userincludes means such as programmable isometric mode means 116 foroperating computer 20 to produce substantially no movement of cable 18resulting from input force exerted by user on handle 16. Means such asprogram isokinetic mode means 118 operates computer 20 to producesubstantially constant speed of motion of cable 18 throughout apredetermined portion of movement resulting from input force exerted onhandle 16 being above a predetermined minimum. Means such as programexternal isotonic mode means 120 operates on computer 20 to limit theresisting force of brake or clutch 42 to a predetermined maximum.Finally, means such as program accommodating isotonic mode means 122operates computer 20 wherein the resisting force of brake or clutch 42is substantially constant as long as the input force exerted by user isat least a predetermined level and wherein the resisting force varies asa function of the force, such as directly proportional to the force or apower of the force exerted, by user when the user force is less than thepredetermined level. Means such as program select operational mode meansselects which of the operating mode means 116, 118, 120 or 122 operatesthe computer.

A select functional mode 126 selects between real-time biofeedback mode128 and a comprehensive analysis mode 130.

Referring now to FIG. 10, a method according to the present inventionfor testing and teaching the lifting capacity and technique of a user isreferred to generally by reference numeral 132. When an accommodatingisotonic mode is selected 122, the weight of an object is determined 136provided the force exerted by user is above a predetermined level. Ifthe user force is below that predetermined level, then the force is withrespect to the user force 138. If the weight of the object is selectedby virtue of the user force being above the predetermined minimum level,then the controller monitors only force in the vertical direction 140.If, on the other hand, the user cannot exert the minimum force, then thecontroller monitors both the vertical and horizontal components of force142 in order to determine both the efficiency of user technique and toprevent possible injury to the user. At that point, the process iscontinuously monitored to see if the user force is above the selectedminimum level 144. If it is, then the velocity is allowed to increase146 just as it would if the user were lifting a real object. If the userforce is not above the selected level, then it is checked to see if itis below the selected level 148. If it is below the selected level, thenthe velocity is decreased 150. If, on the other hand, the user force isnot below the selected level, then at this point it is exactly at theselected level and the velocity is maintained constant 152.

From the foregoing it will be seen that this invention is one welladapted to the attain all the ends and objects hereabove set forth,together with other advantage which are obvious and which are inherentto the apparatus. It will be understood that certain features andsubcombinations are of utility and may be employed without reference toother features and subcombinations. This is contemplated by and iswithin the scope of the claims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the figures of the accompanying drawing isto be interpreted as illustrative and not in a limiting sense.

I claim:
 1. An apparatus for testing and teaching the lifting capacityand technique of a user, comprising in combination:means for acceptinguser input force exerted over a predetermined distance, means forresisting user input force, means for controlling the resisting means,means for operating the controlling means to produce substantially nomovement resulting from input force exerted by a user, means foroperating the controlling means to produce substantially constant speedthroughout a predetermined portion of movement resulting from inputforce above a predetermined minimum exerted by a user, means foroperating the controlling means to limit the resisting force of theresisting means to a predetermined maximum, means for selecting which ofthe means for operating operates the controlling means, and, means foroperating the controlling means wherein the resisting force issubstantially constant as long as the input force exerted by a user isat least a predetermined level and wherein the resisting force varies asa function of the force exerted by a user when the user force is lessthan the predetermined level.
 2. An apparatus according to claim 1further comprising means for substantially eliminating inherent systemresistance to user input force, operably connected to the means foraccepting user input force whereby the force exerted by the resistingmeans substantially equals the force exerted by a user.
 3. An apparatusaccording to claim 2 further comprising means for measuring the distanceover which a user has exerted force, connected in a feedbackrelationship to the controlling means.
 4. An apparatus according toclaim 1 wherein the force accepting means comprises a shaft whichrotates in response to the exertion of user input force over a distanceand wherein the resisting means comprises a magnetic particle unitoperably coupled to the shaft.
 5. An apparatus according to claim 1further comprising means for substantially eliminating inherent systemresistance to user input force, operably connected to the means foraccepting user input force whereby the force exerted by the resistingmeans substantially equals the force exerted by a user.
 6. An apparatusaccording to claim 5 wherein the force accepting means comprises a shaftwhich rotates in response to the exertion of user input force over adistance and wherein the resisting means comprises a magnetic particleunit operably coupled to the shaft, and wherein the resistanceeliminating means comprises a motor operably coupled to the shaft.
 7. Anapparatus for testing and teaching the lifting capacity and technique ofa user, comprising in combination:means for accepting user input forceexerted over a pre-defined distance, means for resisting user inputforce, controlling means for controlling the resisting means, programmeans for operating the controlling means to produce substantially nomovement resulting form input force exerted by a user, program means foroperating the controlling means to produce substantially constant speedthroughout a predetermined portion of movement resulting from inputforce above a predetermined minimum exerted by a user, program means foroperating the controlling means to limit the resisting force from theresisting means to a predetermined maximum, means for selecting which ofthe program means operates the controlling means, and a further programmeans for operating the controlling means wherein the resisting force issubstantially constant as long as the input force exerted by a user isat least a predetermined level and wherein the resisting force varies asa function of the input force exerted by a user when the user force isless than the predetermined minimum.
 8. An apparatus according to claim7 further comprising means for substantially eliminating inherent systemresistance to user input force, operably connected to the means foraccepting user input force whereby the force exerted by the resistingmeans substantially equals the force exerted by a user.
 9. An apparatusaccording to claim 8 further comprising means for measuring the distanceover which a user has exerted force, connected in a feedbackrelationship to the controlling means.
 10. An apparatus according toclaim 7 wherein the force accepting means comprises a shaft whichrotates in response to the exertion of user input force over a distanceand wherein the resisting means comprises a magnetic particle unitoperably coupled to the shaft.
 11. An apparatus according to claim 7further comprising means for substantially eliminating inherent systemresistance to user input force, operably connected to the means foraccepting user input force whereby the force exerted by the resistingmeans substantially equals the force exerted by a user.
 12. An apparatusaccording to claim 11 wherein the force accepting means comprises ashaft which rotates in response to the exertion of user input force overa distance and wherein the resisting means comprises a magnetic particleunit operably coupled to the shaft, and wherein the resistanceeliminating means comprises a motor operably coupled to the shaft.
 13. Amethod for testing and teaching the lifting capacity of a person,comprising in combination the steps of:accepting user input force over apredefined distance; resisting the user input force; controlling theamount of resisting force wherein the resisting force is substantiallyconstant as long as the input force exerted by the person is at least apredetermined level; and controlling the amount of resisting forcewherein the speed of movement resulting from the input force exerted bythe person is proportional to that force when that force is less thanthe predetermined level.